Bauxite, lime and sodium hydroxide are ground and mixed in a ball mill – the mixture turns into a red slurry, which is then conveyed into the pumping tank. Some of the balls from the mill can potentially enter the tank along with the slurry. To prevent this from happening, the balls are collected in a weir arrangement, which overflows into the main tank. Level measurement in the tank avoids dry running of the pump and ensures a continuous process.